This invention relates to self-energized, air-core (SEAC) superconducting motors and more particularly, to such a motor having a multiple winding rotor.
The discovery of high-temperature superconductors (HTS) is expected to greatly impact the design, specific power and efficiency of electric motors. First, high specific power motors can now be designed in which the magnetic materials previously used are eliminated. In such motors, high magnetic fields can be more efficiently generated using superconductive windings. Second, use of HTS materials will significantly reduce winding losses and other eddy current losses. Further, hystersis losses in the magnetic material are also eliminated. Generally, the new design superconducting motors should achieve efficiencies exceeding 95% (for intermediate size motors) compared with the 90% efficiency of conventional motors. The motors are useful in various propulsion system applications.
Conventional synchronous and induction motors are used, for example, as intermediate size motor drives. Generally, the design of these motors is inappropriate for superconducting motors since these designs cannot fully realize the unique properties of superconducting materials. Replacing rotor windings of a conventional three-phase induction motor with a superconducting winding, for example, is not adequate. If the rotor winding has a cross-sectional area large enough to carry induced current without going into normal (steady state) operation, it will produce zero (0) average torque. But, if the rotor winding has a smaller cross-sectional area, it may be driven into its normal operating state in a non-controllable manner during start-up. Use of a three-phase synchronous motor does not create these problems; and, elimination of brushes in such a motor has particular advantages in high speed applications. The motor of this invention operates as a synchronous motor when it reaches steady state operating condition, while the rotor windings are inductively energized and controlled in operation as described hereinafter.